Problem: Solve for $n$ : $n + 20 = -1$
Explanation: Subtract $20$ from both sides: $ \begin{eqnarray} \\ n + 20 &=& -1 \\ \\ {-20} && {-20} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{20 + n} &\hphantom{=}& \hphantom{-1} \\ n &=& -1 {- 20} \\ \end{eqnarray} $ Simplify. $ n = -21$